Pour the mixture into the skillet and cook on low-medium heat until the sides and the majority of the mixture is cooked (15-20 minutes). You can test this by gently shaking the pan to see if it giggles. You want about 2″ of the sides to be moderately firm. It’s okay if the middle is still a bit giggly.

Put the skillet in the oven on a low broil until the top is golden brown and the fritatta doesn’t giggle any more (10-15 minutes).